I have to be honest. As of yesterday I did not knew what these were. I have seen books, and my wife owns beautiful coloring books filled with the most amazing line-art.
Zentangles are used to induce a “zen” state. You are supposed to just start, and let your mind guide you without sketching. It is not ‘allowed’ to erase lines as mistakes are part of life. Normally you start with a “string” on which you guide the patterns.
I googled some YouTube videos and did find some common rules. If you want to make it pleasing to the eye, follow patterns. Your mind expects patterns. Your mind expects lines to continue where they end and shapes to form.
I might buy a book about it some day, as it is so soothing, just to doodle on a rainy day.
The drop-shadow could have been better, but my 6B Pilot Croquis sketch pen left too much of a mark on the paper. I used a smudge pen to make it more even.
These were the tools I used:
I have my smudge pen on the left, new in my arsenal is a Sakura Brush pen which has a sensitive tip to vary width and fill in large areas quickly if needed. I used a Micron 0.4 for the lines, and the sketchpen for the drop shadow. Later on I refined the shadows with a 0.5 B mechanical pencil.
Fun fact, the mechanical pencil I own for at least 20 years now. It has been part of my standard arsenal throughout my life.